Photovoltaic effect involves generation of a potential difference or voltage in a material structure through interaction with photons or light. There are two major areas of applications of the photovoltaic effect. These include: i) detectors of light or photons and ii) electrical power generation. A wide range of inorganic semiconductors are used for photodetector applications at various wavelengths through photovoltaic effect. The solar cell is an example of the application of the photovoltaic effect for power generation. In either of the applications a junction structure (diode) is constructed using the material considered and appropriate interfaces. As photons or a light beam is made incident on this structure, electrons and holes are generated provided the wavelength of the light is sufficiently small (photon energy more than the band gap) and these charges are then swept across the junction due to the built-in electric field at the junction. When these charges reach the opposite electrodes a voltage is produced as the output. This is the basic mechanism of the photovoltaic effect.
As stated earlier, inorganic semiconductors are widely used in photovoltaic applications. Most commercial solar cells are made of silicon. However, these materials are expensive, inflexible, heavy and cannot be made as a large-area solar panel. Recently specific organic/polymeric materials and the combinations of organic/polymeric materials have been shown to exhibit substantial photovoltaic effects. A wide range of applications of these novel materials in light detectors and solar cells have been predicted. In particular, conjugated conductive polymers have been shown to have photovoltaic effect when combined with specific types of electron acceptors such as fullerene (C60). A conjugated polymer is a polymer with alternating double and single bonds between carbon atoms. When a conjugated polymer/C60 composite is irradiated with light an electron is transferred from the polymer to the C60 molecule. If the composite is placed between two metals of dissimilar (high and a low) work functions, the extra electron in the C60 molecule is transported to the metal of the low work function (e.g. aluminum) and the hole created in the conjugated polymer is transported to the metal of high work function (e.g. indium-tin-oxide). Thus a voltage is created between the two metal contacts. Such photovoltaic effect involving conjugated polymers have been widely demonstrated.